Re: [PATCH] net: check for dev pointer being NULL in dev_hard_header() to avoid GPF

[George Kennedy]

Hi Eric,

More info...

On 12/1/2022 11:11 PM, Eric Dumazet wrote:
> On Thu, Dec 1, 2022 at 9:44 PM George Kennedy <george.kennedy@xxxxxxxxxx> wrote:
> > On 12/1/2022 2:25 PM, Eric Dumazet wrote:
> > > On Thu, Dec 1, 2022 at 2:16 PM Pavan Chebbi <pavan.chebbi@xxxxxxxxxxxx> wrote:
> > > > On Wed, Nov 30, 2022 at 7:43 PM George Kennedy
> > > > <george.kennedy@xxxxxxxxxx> wrote:
> > > > > The dev pointer can be NULL in dev_hard_header(). Add check for dev being
> > > > > NULL in dev_hard_header() to avoid GPF.
> > > > >
> > > > > general protection fault, probably for non-canonical address
> > > > >       0xdffffc0000000046: 0000 [#1] PREEMPT SMP KASAN NOPTI
> > > > > KASAN: null-ptr-deref in range [0x0000000000000230-0x0000000000000237]
> > > > > CPU: 1 PID: 45 Comm: kworker/1:1 Not tainted 6.1.0-rc7+ #2
> > > > > Hardware name: Red Hat KVM, BIOS 1.15.0-2.module+el8.6.0+20659+3dcf7c70
> > > > > Workqueue: mld mld_ifc_work
> > > > > RIP: 0010:macvlan_hard_header (./include/linux/netdevice.h:3057
> > > > >       (discriminator 4) drivers/net/macvlan.c:594 (discriminator 4))
> > > > > RSP: 0018:ffff888103d377d0 EFLAGS: 00010212
> > > > > RAX: dffffc0000000000 RBX: ffff88801cf1a000 RCX: 0000000000000000
> > > > > RDX: 0000000000000046 RSI: 0000000000000000 RDI: 0000000000000230
> > > > > RBP: ffff88801e8ef328 R08: 0000000000000000 R09: 0000000000000060
> > > > > R10: 0000000000000000 R11: 0000000000000000 R12: ffff88801f0497c0
> > > > > R13: 0000000000000000 R14: ffff888045187c98 R15: 0000000000000060
> > > > > FS:  0000000000000000(0000) GS:ffff888106c80000(0000)
> > > > >       knlGS:0000000000000000
> > > > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > > CR2: 00007fbf3f1c1840 CR3: 0000000014e36000 CR4: 00000000000006e0
> > > > > Call Trace:
> > > > >    <TASK>
> > > > > neigh_connected_output (./include/linux/netdevice.h:3060
> > > > >       net/core/neighbour.c:1595)
> > > > > ip6_finish_output2 (./include/net/neighbour.h:546
> > > > >       net/ipv6/ip6_output.c:134)
> > > > > ip6_finish_output (net/ipv6/ip6_output.c:195 net/ipv6/ip6_output.c:206)
> > > > > ip6_output (./include/linux/netfilter.h:291 net/ipv6/ip6_output.c:227)
> > > > > NF_HOOK.constprop.0 (./include/net/dst.h:445
> > > > >       ./include/linux/netfilter.h:302)
> > > > > mld_sendpack (net/ipv6/mcast.c:1824)
> > > > > mld_send_cr (net/ipv6/mcast.c:2122)
> > > > > mld_ifc_work (net/ipv6/mcast.c:2655)
> > > > > process_one_work (kernel/workqueue.c:2294)
> > > > > worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2437)
> > > > > kthread (kernel/kthread.c:376)
> > > > > ret_from_fork (arch/x86/entry/entry_64.S:312)
> > > > >    </TASK>
> > > > > Modules linked in:
> > > > > Dumping ftrace buffer:
> > > > >      (ftrace buffer empty)
> > > > > ---[ end trace 0000000000000000 ]---
> > > > >
> > > > > Fixes: 0c4e85813d0a ("[NET]: Wrap netdevice hardware header creation.")
> > > > > Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
> > > > > Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx>
> > > > > ---
> > > > >    include/linux/netdevice.h | 2 +-
> > > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > > > > index eddf8ee270e7..9b25a6301fa5 100644
> > > > > --- a/include/linux/netdevice.h
> > > > > +++ b/include/linux/netdevice.h
> > > > > @@ -3054,7 +3054,7 @@ static inline int dev_hard_header(struct sk_buff *skb, struct net_device *dev,
> > > > >                                     const void *daddr, const void *saddr,
> > > > >                                     unsigned int len)
> > > > >    {
> > > > > -       if (!dev->header_ops || !dev->header_ops->create)
> > > > > +       if (!dev || !dev->header_ops || !dev->header_ops->create)
> > > Do  you have a repro ?
> > See syzkaller repros attached.
> >
> > > This patch will not prevent a crash later I think.
> > The repro ran overnight without failure with the patch applied.
> Yes, but the patch is hiding a potential bug that might show up with
> other 'repros'
The repro fails when these devices are configured (seem like small mtu):

20: vxcan0@vxcan1: <NOARP,UP,LOWER_UP> mtu 72 qdisc noqueue state UP group default qlen 1000
    link/can
    inet 172.20.20.38/24 scope global vxcan0
       valid_lft forever preferred_lft forever
21: vxcan1@vxcan0: <NOARP,UP,LOWER_UP> mtu 72 qdisc noqueue state UP group default qlen 1000
    link/can
    inet 172.20.20.39/24 scope global vxcan1
       valid_lft forever preferred_lft forever


# diff ../config.fail .config
3325c3325
< CONFIG_CAN_VXCAN=y
---
> # CONFIG_CAN_VXCAN is not set

Thanks,
George

> > > Please fix the root cause, thanks !
> > Will try.
> Thanks, having a repro definitely should help to find the real bug.
>
> I took a look at macvlan , and could not see how vlan->lowerdev  could
> be NULL in the first place.
>
> > Thanks,
> > George
> > > > >                   return 0;
> > > > net_device being NULL during eth header construction? seems like a
> > > > more serious issue?
> > > > If it indeed is a genuine scenario I think a better description is needed...
> > > >
> > > > >           return dev->header_ops->create(skb, dev, type, daddr, saddr, len);
> > > > > --
> > > > > 2.31.1